This invention relates generally to the tracking of vehicle motion, and more particularly, to the utilization of redundant vehicle state information and clinometers to provide accurate measurements of the vehicle state in real time.
The interest in the tracking of land vehicles has recently increased dramatically. Vehicle tracking is an applied science which utilizes a variety of techniques and approaches to determine vehicle state information. The vehicle state information may include present position, velocity, acceleration as well as attitude information.
For centuries, the position and course of ships were determined by celestial observations and compass readings. Subsequently, similar technology was utilized for aircraft navigation. More recently, radio location systems, inertial measurement systems (IMS), and Global Positioning Systems (GPS) have been utilized to assist with the tracking and navigation of vehicles. In addition, map matching has also been introduced to reduce time based error in vehicle tracking and navigation systems.
Vehicle tracking and navigation systems provide an abundance of useful information related to the vehicle state. This information may be utilized by the driver for planning the best possible route to reach a particular destination and may include distance and direction information as well as detailed guidance instructions.
Additionally, the vehicle tracking systems may be utilized in a fleet management system wherein a central control facility remotely monitors the status of individual vehicles. Typical applications include bus schedule control, police car dispatching, and emergency car dispatching. Location and status data may be transmitted between the plurality of vehicles and the central control facility via radio communication.
Inertial measurement units or guidance systems were developed in Germany during the Second World War. These initial inertial systems were generally utilized for determining desired flight attitude in aircraft and measuring acceleration or thrust along a longitudinal axis.
More recently, inertial measurement units have been utilized to assist with the tracking and navigation of land vehicles. Specifically, inertial measurement units can monitor the acceleration vector of a land vehicle in motion. The inertial measurement units generally consist of various combinations of inertial sensors including one to three gyros and one to three accelerometers. Additional sensors may be utilized to provide fault tolerant operation.
The gyros used in the inertial measurement unit measure the angular velocity of the vehicle with respect to inertial space and the accelerometers measure the linear acceleration of the vehicle. The angular orientation of the vehicle may be obtained by integrating the output of the gyros with respect to time. The linear velocity and position of the vehicle may be obtained by integrating the accelerometer output with respect to time and performing appropriate coordinate transformations.
Some tracking subsystems such as dead reckoning or inertial measurement systems inherently accumulate error over time. While this error may be reduced through various error collapsing schemes, the accuracy of the entire vehicle tracking system will be drastically improved if the error is minimized before the vehicle begins to move.
Other errors may arise in the vehicle tracking subsystems due to noise in the tracking instruments, processing limitations and errors in the map database if map matching is utilized. Therefore, the accuracy of the vehicle tracking system is greatly improved if an increased amount of vehicle state information, including redundant vehicle state information, is utilized by the vehicle tracking system.